In exercising different muscles there are a number of muscle structures which traverse two different joints of the body and assist in movement about those joints, and such movements are customarily referred to as double joint muscle movements. For example, the biceps flex and supinate the forearm at the elbow and flex the upper arm at the shoulder. Other muscles which perform similar functions are the triceps, quadriceps and hamstrings. In exercising the double joint muscles, the resistance provided by cam and free weight types of equipment do not fully meet the needs of the athlete, and in the past the inertial devices have not met various resistance needs and particularly in order to fully and appropriately stress a given muscle throughout its entire range of movement.
In terms of correct resistance, an appropriate force must be developed which increases or decreases commensurate with the athlete's changing potentials throughout the course of exercise; for example, as successive repetitions are performed, the fatigue factor will play an important part and dictate variations in resistance to muscle movement. For this reason, it is important to compensate for any decaying effect throughout the latter portions of successive movements.
Research consistently demonstrates that, due to fatigue, the force an athlete can exert during a series of movements changes in relative pattern and level. In particular, as successive repetitions are performed, the athlete's force generating capabilities decrease or "differentially decay" faster during the latter portions of such movements.
In my prior U.S. Pat. No. 4,863,161, a combination of inertial resistance and isokinetics was relied upon to a great extent to provide correct resistance to muscle movement. Other devices which have operated on similar principles are disclosed in U.S. Pat. Nos. 3,573,865 to Annas and 4,650,185 to Cartwright. U.S. Pat. No. 3,573,865 to Annas is representative of numerous exercise machines which have been devised in the past and which employ a linear force actuator but do not compensate for the differential decaying effect which typically occurs as successive repetitions are performed by the exerciser.
It is therefore desirable to provide an inertial resistance which meets the varied and changing demands of the athlete without resorting to the use of artificial means of resistance, such as, isokinetic or electrical clutch mechanisms and which will most efficiently compensate for any differential decaying effect.